The present invention relates in general to low drop out drivers and, more particularly, to low drop out drivers requiring low quiescent current with improved dynamic performance.
Most, if not all, electronic devices require some sort of power supply in order to operate. Additionally, many of the electronic devices require a regulated, Direct Current (DC) power source. The DC power source is generally derived, for example, from an Alternating Current (AC) source using a rectification circuit or from a DC power supply, such as a battery. In either case, a linear regulator is often used to supply the regulated output potential to the electronic device, using a P-Type Metal Oxide Semiconductor Field Effect Transistor (PMOSFET) to control current through a resistive ladder to ultimately provide the regulated output voltage. The driver is useful to provide high input and low output impedance which is used to isolate the regulation circuit from loading effects caused by the electronic circuit deriving power from the regulation circuit.
Some prior art drivers utilize an N-Type Metal Oxide Semiconductor Field Effect Transistor (NMOSFET) source follower in series with a constant current source to provide the gate drive voltage to the PMOS power transistor from the source terminal of the NMOSFET. The NMOSFET source follower driver provides adequate current drive to charge the gate of the PMOS power transistor, but the constant current source does not provide adequate discharging capability to turn the PMOS power transistor off in a short amount of time. Another prior art solution is to provide a constant current source in series with the NMOSFET such that the current source provides the charging current to the PMOS power transistor and the NMOSFET provides the discharging current, in which case, a slow charging current is produced with a fast discharging current. In addition, prior art drivers do not produce output voltages close enough to the top and bottom supply rails and therefore deliver poor drop out performance.
Hence, there is a need for a driver circuit which provides adequate dynamic performance in combination with low drop out operation.